Batass

Mighty demon blow through (no blower on yet)
MSD distrib, coil, box
custom msd wires
Comp xr288hr

I tried starting my new engine last night and it just backfired, moving the distributor around just made it backfire either out the header or carb. Sometimes I hear two cylinders fire.
Checking the timing with a light is hard, it usually only flashes two or three times and no more. But it does appear to be 10*. Battery is about dead, I'm thinking maybe it doesnt have the juice to power the ignition system.
Everything is wired up correctly and it does have spark.
I didnt take the carb apart, so I dont know if all is well in there. Dont even know what the jetting is, but it should at least fire up right?????
Ive never had this problem before......

onfire

batass,

So you know you have spark. Since you are hearing it back fire means that you are close. Try to start again from the tdc of #1 and drop the dissy again might be off by one tooth if your hearing it backfire at your present setting.

Check to make sure your jets aren't clogged and that your primaries are opening up enough just as a precaution. Easy way to tell if your carb is getting gas (fuel pump test) is to disconnect the fuel line and lead it down to a pan or a can or empty oil quart and just turn the motor over.

Don't worry about timing till you get it fired up. Then apply the desired timing.

Rabi C.

Batass

I was sure I had the timing right, but I thought maybe there was a chance I was 180 off, so I swapped the wires around, double checked the firing order, and it made similiar backfiring sounds. Out the carb and exhaust, both times.
Charged the battery up. Even swapped different plug wires.
Maybe it is a tooth off...If it was carb issues, it wouldnt make the same sounds with the wires on the dizzy 180 off....right?
Even with carb problems, it should run for a second at least....
Has fuel, the squirters squirt and bowls are filled correctly. (sight glass)
Also checked my grounds and all is good.
Tomorrow I'll pull the dizzy and start over.
But I checked it with a timing light and set it to 20* also. It sounded like it wanted to run....hell IDK Im missing something somewhere.
The cam was installed and degreed by a great shop, so I doubt any issue there.
Brand new dizzy, brand new coil.
I'm pulling my hair out, ahhhhhhhhhh

cheppibear

Had this problem before when I cam swapped in my 1984. Was banging my head for a long time since I am pretty good with valve timing and distributor installations.

Problem was that my valve adjustment was too tight so in essentially both the intake and exhaust valves were open slightly in every cylinder on TDC. The resulting spark blew the bang right up through the carb (it was like someone fired a shotgun in the garage).

1. Do a compression to make sure you have good psi across the board.
2. RE-adjust your valves.
3. RE-install the distributor is necessary.

I readjusted my valve lash and she fired right up. I was used to the adjustment on the old cam.

shootryan

this sounds similar to the problem i am having, how do i go about adjusting the valves? the timing is weird with my 85 camaro 383. I adjusted the distributor one before (couple teeth off) and it was running great.. came out the next morning and it wouldnt start... i would turn over however. i dont know what to do

Batass

I have hydraulic roller lifters though, and I only turned them a half turn. I'll do a compression check though. Its a big cam.
I put the timing light on it and its perfect!????If the Number 1 cylinder is timed right, the rest have to follow. Theres no way anything can be off.....
Backfire, backfire, backfire.

Is it possible a very poorly tunded carb could do this???

ibmtech

iTrader: (1)

There are several ways that people like to adjust their valve.. Some use the EOIC method. This is where as the exhaust valve is just starting to open you adjust the intake valves and then when the intake valve is just starting to close you adjst the exhaust.

I have heard other people turn the engine over 1/4 turn and adjust like 8 valves that are all closed.. Sorry don't know the sequence then turn the engine 1/2 turn and adjust the other 8 valves..

Here is what I did on mine the 1st time which worked. With a cold engine, I did the EOIC method.

Loosen the Rocker nut until the push rod twists easily in your fingers. Then tighten to rocker nut down till you can't twist it any more. You will notice that if you turn the engine over a few more revolutions the 1st one will twist easily in your fingers again. When your oil pump fills up your lifters they will take up the slack. That should get your real close.

Batass

The rocker/valve/lifters are adjusted properly. I did check and loosened a few and retightened to make sure. My engine builder also thought the same thing. Then I checked compression on all cylinders. If they were too tight and a valve was stuck open, I'd see a loss of compression.......
Swapped carbs just for fun, no change.
Rechecked timing and all wire connections.

Fuel, spark, compression all good..............

There are two things I can think of.

1. With a cam this large, xr288hr, 236/242 duration i think, 110 lsa, does the motor need to spin well to start?? It seems a little slow, starter is a little tight, and the battery is kinda old.

2. Cam timing? Could the shop have possibly incorrectly timed the cam when they degreed it?? I dont hear any valves hitting pistons.....

Still pulling hair....thanks for the replies

cheppibear

Your firing order is 1-8-4-3-6-5-7-2 correct?

Make sure the wires are not touching each other and fairly separated.

Batass

Yea right firing order, and clockwise, the wires are touching.......but ive never had problems with touching wires, and these are msd super something wires....
Tonight when its dark, I'll turn it over and look to see if i see any lightning bolts.

Supervisor42

Stop farting around and get that thing running! Birth that baby!
Back off all of the valve rockers a complete round. This will give you near stock lift and duration. Get some heat to the starter, new battery and charger or friend's car with jumper cables.
Block the throttle open 1/4" and blitz the accelerator pump while it's spinning.
If you get big fireballs your ignition timing is off.
Sort out the cam/valve adjustments when you get it run in.

Batass

I gave the lifters a 1/2 turn preload. Heard today that these comp ones may not need preload, but actually a gap. Heard of this?? (hyd roller) Timing is right, so a valve (or valves) isnt functioning correctly. Hope it wasnt the cam install....

battyice

A blow-through carb won't run correctly on a NA engine. Before you go any further, try starting it with regular carb. If possible, borrow one from a buddies engine that you know starts and runs :-)

Batass

I found the problem. I believe a blow through carb will work ok na as long as your not in the secondaries. The primary side is mostly the same as na carb.

Anyway, I'm a big idiot. I had the firing order on the engine wrong, right on the distributor.

Somehow I thought it was 1-4 on the driver side and 5-8 on the passenger. I was so sure of it that when I questioned it, I threw it out the window, until I realized that it was either that or the cam......

Someone must've slipped me some crack when I wasnt looking....